1. Field of the Invention:
The present invention relates to an electrical noise suppressor for suppressing electrical noise generated by a direct current motor.
2. Related Art:
Conventionally, a wiper driving device for driving a wiper of a vehicle comprises a motor unit and a gear unit. A worm gear attached to a rotation shaft of a motor of the motor unit is engaged with a gear wheel in the gear unit to rotate the gear wheel therewith. Further, the rotation shaft is connected with a crank arm for driving the wiper so that rotation of the motor is transmitted to the crank arm, thereby driving the wiper.
In the wiper driving device, the motor is a direct current type (DC motor) which has brushes and an armature. The brushes are connected to an external power source through electrical terminals. When the brushes make contact with a commutator of the armature, the DC motor is supplied with power. However, when the motor operates, the brushes sliding on the commutator generate electrical noise. Therefore, the DC motor has an electrical noise suppressor for restricting electrical noise from being transmitted to the external power source through the terminals.
As shown in FIG. 14, an electrical noise suppressor 50 for a DC motor is disposed in a brush holder 51 for holding brushes (not shown) of the DC motor. The electrical noise suppressor 50 has, for each brush, a choke coil 52 wound around a core 58 and a grommet 53 in which the choke coil 52 is accommodated. One end of the choke coil 52 is connected to the brush through an electrical connector 54 and a pigtail 55 connected to the brush. The other end of the choke coil 52 is connected to an external power source (not shown) through an electrical connector 56 and an electrical terminal 57. Thus, the choke coil 52 is connected between the brush and the terminal 57. Electrical noise generated by the brush is damped by the choke coil 52.
However, the choke coil 52 is disposed in the grommet 53 in such a manner that the choke coil 52 hangs in the air. Therefore, positions of the choke coil 52 and the connectors 54, 56 tend to greatly vary. As a result, chattering of the choke coil 52 may occur due to vibration caused by operation of the motor. To overcome this problem, an opening between the pigtail 55 and a motor yoke (not shown) of the motor, windings or a commutator of an armature of the motor is increased so that the pigtail 55 does not make contact with the motor yoke, the windings and the commutator of the armature during operation of the motor. However, in this case, a usable space within the motor is decreased. Further, due to this space limitation, it is difficult to increase inductance of the choke coil 52.
Further, in the electrical noise suppressor 50, the choke coil 52 tends to loosen and the core 58 of the choke coil 52 tends to come off due to vibration caused by operation of the motor. As a result, noise suppressing performance of the electrical noise suppressor 50 may be lessened.
Furthermore, since assembly efficiency for attaching the choke coil 52 and the connector 56 to the grommet 53 is poor, the choke coil 52 and the connector 56 may be bent during assembly.